The invention relates to a transistor cell, to a transistor, in particular to a lateral transistor having a high current-carrying capacity, to a method for producing a transistor as well as to a diode.
Due to a contact between a gallium nitride (GaN) layer and an aluminum gallium nitride (AlGaN) layer, gallium-nitride-based transistors may have a highly conductive layer at the AlGaN/GaN interface that can be used as a transistor channel of a field-effect transistor. The conductive layer is contacted via two metal faces that are deposited on the semiconductor surface and represent the source and the drain of the transistor. A control electrode deposited between the source and the drain onto the surface is used as a gate of the field-effect transistor. Such a construction is characterized in that all three transistor terminals are accessible via the top side of the semiconductor and in that the current in the transistor channel flows parallel to the semiconductor surface. Such a transistor construction is referred to as lateral component. In contrast thereto, many transistors (e.g., in silicon technology) are designed as vertical components, wherein at least one transistor terminal, usually the source or the drain, can be contacted from the lower side of the semiconductor substrate.
The development of GaN-based field-effect transistors having a gate made of a Schottky metal (HEMT) or having a gate made of a metal insulated by a dielectric (MISFET) is well advanced for applications as microwave amplifiers. Typically, such components have gate widths of less than 100 mm, wherein the arrangement of the source, drain and gate electrodes on the semiconductor surface is determined by the peculiarities of electric signal propagation in the frequency range of microwaves and results in alternating source fields and drain fields that are arranged one below the other and between which the gate electrodes are arranged. Usually, the gate electrodes are electrically conductively connected to each other on one side thereof at the side of the source fields and drain fields.
The development of GaN-based transistors as switching transistors in the field of power electronics is less advanced. In this field, transistors having a higher pulse-current-carrying capacity (typically, more than 50 A) and having a greater gate width (typically, more than 100 mm) are required. Since the desired switching frequencies in the field of power electronics are much lower than 1 GHz and the length of the electromagnetic waves can thus be considered as being very large as against the transistor dimensions, there is more freedom with regard to the arrangement of the source, drain and gate electrodes on the semiconductor surface.
Thus, it is obvious that the lateral construction of a GaN-based transistor for switching in the field of power electronics may differ from the construction of a GaN-based microwave transistor as well as from the construction of a vertical switching transistor for power electronics. Attention must be particularly turned to the efficient use of the semiconductor surface since the costs per semiconductor surface are particularly high with GaN-based semiconductors.